Polycarbonates are well known amorphous polymers known for their transparency, toughness, and impact resistance. Copolyestercarbonates are also well known. These polymers having both ester and carbonate linkages of the properties which are similar to polycarbonates. A new copolyestercarbonate has been described in Ser. No. 07/627,517 filed Dec. 14, 1990, Ser. No. 07/476,068 filed Jan. 30, 1990 and Ser. No. 07/455,118 filed Dec. 22, 1989. This copolyestercarbonate has aromatic carbonate units and aromatic aliphatic ester units wherein the aromatic unit is a dihydric phenol and the ester unit is an aliphatic alpha omega dicarboxylic acid. This substantially differs from the totally aromatic copolyestercarbonates which are well known from the prior art particularly U.S. Pat. No. 4,522,980 and other relevant patents. As is observed from the data on the copolyestercarbonate of this invention it has the advantage of better flow and processability at a lower temperature than an ordinary aromatic polycarbonate of the same intrinsic viscosity. However heat related properties of the copolyestercarbonates such as DTUL are lowered. It has now been found that by blending aromatic polycarbonate with the copolyestercarbonate disclosed herein over a specific weight percent range, certain physical properties change over the range while other properties demonstrate very little if any change over the range.